The present invention relates to a method for manufacturing a group III-V compound semiconductor useful for a light-emitting device, and the like, represented by the general formula In.sub.x Ga.sub.y Al.sub.z N (where x+y+z=1, 0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, and 0.ltoreq.z.ltoreq.1).
2. Description of the Related Art
There has been known a group III-V compound semiconductor represented by the general formula In.sub.x Ga.sub.y Al.sub.z N (where x+y+z=1, 0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, and 0.ltoreq.z.ltoreq.1) as a material for a light-emitting device such as an ultraviolet, blue, or green light-emitting diode, or an ultraviolet, blue, or green laser diode. Hereinafter, in some cases, the x, y, and z in the general formula may be referred to as InN mixed crystal ratio, GaN mixed crystal ratio, and AlN mixed crystal ratio, respectively. In the group III-V compound semiconductors, especially with the one containing 10% or more of InN mixed crystal ratio, the emission wavelength in a visible region can be regulated in accordance with the InN mixed crystal ratio, and hence it is especially important for the display applications.
Examples of the manufacturing method of the group III-V compound semiconductor include molecular-beam epitaxy (hereinafter, may be referred to as MBE) method, metalorganic vapor phase epitaxy (hereinafter, may be referred to as MOVPE) method, and hydride vapor phase epitaxy (hereinafter, may be referred to as HVPE) method. Among these methods, MOVPE method enables the uniform crystal growth over a large area, and hence it is important.
There are known Be, Ca, Mg, Zn, C, and the like as acceptor type dopants for imparting the p-type conductivity to the compound semiconductor. Of these, Mg is capable of implementing higher p-type conductivity than other dopants, and hence it is widely used at present. The following description will be given by taking Mg as an example, however, it is well known that there occur the same troubles with the other p-type dopants.
As Mg sources for use in MOVPE method, there are known bis-cyclopentadienylmagnesium ((C.sub.5 H.sub.5).sub.2 Mg, hereinafter, may be referred to as Cp.sub.2 Mg), bis-methylcyclopentadienylmagnesium ((C.sub.5 H.sub.4 CH.sub.3).sub.2 Mg, hereinafter, may be referred to as MCp.sub.2 Mg), bis-ethylcyclopentadienylmagnesium ((C.sub.5 H.sub.4 C.sub.2 H.sub.5).sub.2 Mg, hereinafter, may be referred to as ECp.sub.2 Mg), and the like. Any of these will be strongly adsorbed on gas piping, a reactor, and the like, and hence the incorporation of the dopants into crystal starts with a delay after the supply of a dopant source. Also, there occurs a trouble that the incorporation of dopants is gradually caused unintentionally in the following runs after the growth in which a dopant source has been flown. These are generally referred to as the memory effect of a dopant.
The large deficiency of the memory effect is especially in that the layer required to be highly pure for use in the emitting layer of a light-emitting device is doped unintentionally with a dopant, and it makes difficult to obtain a layer having a desired quality. These dopant sources react with the materials constituting gas piping or a reactor, after which impurities are gradually released from the materials, also causing a trouble that a layer having a desired high quality cannot be grown. Further, in large equipment of industrial importance, a large amount of dopant source must be supplied, and hence these troubles have been particularly serious problems.